On Pá 11-03-05 02:25:07, Adam Belay wrote: > On Thu, 2005-03-10 at 11:28 -0500, Alan Stern wrote: > > On Wed, 9 Mar 2005, Adam Belay wrote: > > > > > > This partly a question of definitions and usage. However, if a parent's > > > > change of state can be made transparent to the child device driver (i.e., > > > > the parent resumes automatically whenever the child driver tries to do > > > > anything), then why shouldn't the parent suspend itself without suspending > > > > the child? > > > > > > I think your not drawing a distinction between physical and logical > > > (class) devices. A physical device can be turned off, but the logical > > > child device is allowed to remain on. However, A physical child to a > > > physical device must be powered off before the parent. Perhaps this was > > > your intention? > > > > Normally yes, I agree, we will want to suspend children before parents. > > But your argument isn't valid; a physical child to a physical device might > > very well have its own external power supply. Then it wouldn't be > > necessary for the child to be off at the time the parent is turned off. > > Consider a USB disk drive as an example. If it plugs into the wall then > > it doesn't need to be spun down when its USB hub is suspended. > > > > Of course if you want to power down both devices, then certainly the child > > should be turned off first. > > > > Alan Stern > > This is why I'm in favor of power domains (power parents and children > that can be independent of physical device relations). Power domains > are common for internal devices, not just external devices. Still, if > you disable a physical parent, then the device is no longer operational. > Disable the usb host controller, and the external disk drive cannot be > used (in fact data may be lost). So it's necessary to stop every child > device first, and generally also power it off if we can control the > power source. I just don't see it like that. Remember old scsi disks where formatting took half an hour? You may do something like invoke scsi format operation power down usb controller <half an hour later> power up usb controller get the results Now, that was probably bad example, but I do think some devices might do usefull work even with their parents disabled. Pavel -- People were complaining that M$ turns users into beta-testers... ...jr ghea gurz vagb qrirybcref, naq gurl frrz gb yvxr vg gung jnl!
